Inhibition of F1-ATPase Rotational Catalysis by the Carboxyl Terminal Domain of the ε Subunit [Enzymology]
September 16th, 2014 by Nakanishi-Matsui, M., Sekiya, M., Yano, S., Futai, M.
Escherichia coli ATP synthase (FoF1) couples catalysis and proton transport through subunit rotation. The ϵ subunit, an endogenous inhibitor, lowers F1-ATPase activity by decreasing the rotation speed and extending the duration of the inhibited state (Sekiya, M., Hosokawa, H., Nakanishi-Matsui, M., Al-Shawi, M. K., Nakamoto, R. K., Futai, M. (2010) J. Biol. Chem. 285, 42058-42067). In this study, we constructed a series of ϵ subunits truncated successively from the carboxyl terminal domain (Helix1/Loop2/Helix2), and examined their effects on rotational catalysis (ATPase activity, average rotation rate, and duration of inhibited state). As expected, the ϵ subunit lacking Helix2 caused about ½-fold reduced inhibition, and that without Loop2/Helix2 or Helix1/Loop2/Helix2 showed a further reduced effect. Substitution of ϵS108 in Loop2 and ϵY114 in Helix2, which possibly interact with the β and γ subunits, respectively, decreased the inhibitory effects. These results suggest that the carboxyl terminal domain of the ϵ subunit plays a pivotal role in inhibition of F1 rotation through interaction with other subunits.